Apparatus, method and system for sparse detector

ABSTRACT

An apparatus, system, and method involving one or more sparse detectors are provided. A sparse detector may include an array of scintillator crystals generating scintillation in response to radiation and an array of photodetectors generating an electrical signal in response to the scintillation. A portion of the scintillator crystals may be spaced apart by substituents or gaps. The distribution of the substitutes or gaps may be according to a sparsity rule. At least a portion of the array of photodetectors may be coupled to the array of scintillator crystals. An imaging system including an apparatus that may include one or more sparse detectors is provided. The imaging system may include a processor to process the imaging data acquired by the apparatus or system including the one or more sparse detectors. The method may include preprocess the acquired image data and produce images by image reconstruction.

CROSS-REFERENCE TO THE RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No. 15/029,228, filed on Apr. 13, 2016, which is a U.S. national stage entry under35 U.S.C. §371 of International Application No. PCT/CN2015/100069, filedon Dec.31, 2015, the contents of which are hereby incorporated byreference in their entireties.

TECHNICAL FIELD

This application relates to an imaging technology, and moreparticularly, to a sparse detector and an imaging method and systemusing a sparse detector.

BACKGROUND

A scintillator is a material that may exhibit scintillation. Ascintillator may absorb ionizing radiation and emit a fraction of theabsorbed energy as light. For example, an incoming particle, such as agamma photon, incident on the scintillator may create an energizedelectron, either by Compton scattering or by photoelectric absorption;as the energized electron passes through the scintillator, it may loseenergy and excite one or more other electrons; the excited electron(s)may decay to the ground state, giving off light. As such, thescintillator may produce photons of visible or ultraviolet lightcorresponding to incoming particles that interact with the scintillatormaterial. The intensity of the light pulses may be proportional to theenergy deposited in the scintillator by the incoming particles.

A detector may be formed by coupling a scintillator to an electroniclight sensor, i.e. a photodetector. Detectors are widely used inradiation detection in many fields including, for example, HomelandSecurity radiation detection, neutron and high energy particle physicsexperiments, new energy resource exploration, X-ray detection, nuclearcameras, gas exploration, etc. Merely by way of example, detectors arealso widely used in medical imaging technology such as ComputedTomography (CT) and Positron Emission Tomography (PET).

Scintillators used in, for example, the medical imaging technology, maybe manufactured with materials containing rare earth elements such as,for example, Lanthanum, Lutetium, Yttrium, etc. Scintillators containingrare earth elements may be expensive due to factors including, forexample, the difficulty of crystallization, the scarcity of economicallyexploitable ore deposits, etc. The costs for an apparatus, system and/ormethod involving one or more scintillators may be high. Therefore, it isdesired to lower the costs of such an apparatus, system and/or methodlower costs.

SUMMARY

In a first aspect of the present disclosure, an apparatus is provided.The apparatus may include a sparse detector. The sparse detector mayinclude an array of scintillator crystals generating scintillation inresponse to radiation. At least a portion of the scintillator crystalsmay be spaced apart according to a sparsity rule. The sparse detectorsmay further include an array of photodetector elements configured togenerate an electrical signal in response to the scintillation. At leasta portion of the array of photodetector elements may be coupled to thearray of scintillator crystals.

In some embodiments, at least a portion of the array of scintillatorcrystals may be spaced apart by one or more blocks of alight-transmitting material. In some embodiments, the size of at leastsome of the one or more blocks of the light-transmitting material may besubstantially equal to the size of a scintillator crystal of the arrayof scintillator crystals. In some embodiments, the light-transmittingmaterial may include glass.

In some embodiments, the apparatus may include a gap between twoscintillator crystals of the array of scintillator crystals. In someembodiments, the size of the gap may be substantially equal to the sizeof one scintillator crystal of the array of scintillator crystals.

In some embodiments, at least a portion of scintillator crystals arespaced based on a sparsity rule. In some embodiments, the sparsity rulemay designate a way of substituting scintillator crystals in anon-sparse detector with substituents according to a sparsity rule toobtain a sparse detector. For illustration purposes, a sparsity rule maybe described by comparing a sparse detector to a non-sparse detector.Compared to a non-sparse detector, a sparse detector according to asparsity rule may be formed by substituting at most one scintillatorcrystal out of every two neighboring scintillator crystals, with asubstituent, among the array of scintillator crystals. The descriptiondoes not suggest that to form a sparse detector, a non-sparse detectoris formed, and some scintillator crystals are removed from thenon-sparse detector to make room for substituents or gaps.

In alternative embodiments, the sparsity rule may specify a sparseness.In some embodiments, a sparsity rule that may be applied to the sparsedetector may specify a sparseness of 1% to 50%, or 10% to 40%, or 20% to30%.

In some embodiments, the shape of the sparse detector may be a block, anarc, a ring, a rectangle, or a polygon. In some embodiments, theapparatus may include one, two, or more sparse detectors. In someembodiments, the apparatus may include two sparse detector modulesparallel to each other, a detector module including a plurality ofsparse detectors. In some embodiments, the apparatus may includedetector modules forming a polygon, a detector module including aplurality of sparse detectors. In some embodiments, the apparatus mayinclude sparse detectors forming a ring.

In a second aspect of the present disclosure, an imaging system isprovided. The imaging system may include an apparatus including one ormore sparse detectors that may generate imaging data. A sparse detectormay include an array of scintillator crystals generating scintillationin response to radiation. At least a portion of the scintillatorcrystals may be spaced apart. The sparse detectors may further includean array of photodetector elements configured to generate an electricalsignal in response to the scintillation. At least a portion of the arrayof photodetector elements may be coupled to the array of scintillatorcrystals. The imaging system may further include a processor configuredto generate, based on the imaging data, an image.

In some embodiments, the imaging system may be a single modality imagingsystem. The single modality imaging system may include a CT system, aPET system, a Digital Radiography (DR) system, a Single Photon EmissionComputed Tomography (SPECT) system, an X-ray scan, and an ultrasoundscan. In some embodiments, the imaging system may be a multi-modalityimaging system. The multi-modality imaging system may include a ComputedTomography-Positron Emission Tomography (CT-PET) system, a ComputedTomography-Magnetic Resonance Imaging (CT-MRI) system, a PositronEmission Tomography-Magnetic Resonance Imaging (PET-MRI) system, aSingle Photon Emission Computed Tomography-Positron Emission Tomography(SPECT-PET) system.

In a third aspect of the present disclosure, a method is provided. Themethod may include providing an apparatus including a sparse detector,acquiring imaging data using the apparatus, preprocessing the imagingdata and obtaining preprocessed imaging data, and reconstructing animage based on the preprocessed imaging data. The sparse detector mayinclude an array of scintillator crystals generating scintillation inresponse to radiation. At least a portion of the scintillator crystalsmay be spaced apart. The sparse detectors may further include an arrayof photodetector elements configured to generate an electrical signal inresponse to the scintillation. At least a portion of the array ofphotodetector elements may be coupled to the array of scintillatorcrystals.

In some embodiments, the preprocessing step may further includegenerating virtual scintillator units according to the sparsity rule ofthe sparse detector, calculating the efficiency of the virtualscintillator units, and calculating the efficiency of the line ofresponse (LOR).

Additional features will be set forth in part in the description whichfollows, and in part will become apparent to those skilled in the artupon examination of the following and the accompanying drawings or maybe learned by production or operation of the examples. The features ofthe present disclosure may be realized and attained by practice or useof various aspects of the methodologies, instrumentalities andcombinations set forth in the detailed examples discussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is further described in terms of exemplaryembodiments. These exemplary embodiments are described in detail withreference to the drawings. These embodiments are non-limiting exemplaryembodiments, in which like reference numerals represent similarstructures throughout the several views of the drawings, and wherein:

FIG. 1 is an illustration of an imaging system according to someembodiments of the present disclosure;

FIG. 2 is a flowchart illustrating a process for an imaging methodaccording to some embodiments of the present disclosure;

FIG. 3 is a block diagram illustrating the configuration of an imagingdevice according to some embodiments of the present disclosure;

FIG. 4 is a flowchart illustrating a process for obtaining imaging datawith an imaging device according to some embodiments of the presentdisclosure;

FIGS. 5A through 5D illustrate various configurations of an apparatusaccording to some embodiments of the present disclosure; specifically,FIG. 5A illustrates an apparatus including two detector modulesaccording to some embodiments of the present disclosure, FIG. 5Billustrates a apparatus including four detector modules according tosome embodiments of the present disclosure, FIG. 5C illustrates anapparatus including eight detector modules according to some embodimentsof the present disclosure, and FIG. 5D illustrates an apparatusincluding a plurality of detectors forming a ring according to someembodiments of the present disclosure;

FIGS. 6A through 6B illustrates the configurations of scintillators in adetector according to some embodiments of the present disclosure;specifically, FIG. 6A illustrates a non-sparse detector according tosome embodiments of the present disclosure, and FIG. 6B illustrates asparse detector according to some embodiments of the present disclosure;

FIGS. 7A through 7B illustrate the direct and indirect coupling betweenthe scintillator and the photodetector according to some embodiments ofthe present disclosure; specifically, FIG. 7A illustrates the indirectcoupling between the scintillator and photodetector according to someembodiments of the present disclosure, and FIG. 7B illustrates thedirect coupling between the scintillator and photodetector according tosome embodiments of the present disclosure;

FIGS. 8A through 8C illustrate the one to one coupling between thescintillator and the photodetector according to some embodiments of thepresent disclosure; specifically, FIG. 8A illustrates the one to onecoupling between the scintillator and the photodetector in a lateralview according to some embodiments of the present disclosure, FIG. 8Billustrates the one to one coupling between a scintillator crystal and aphotodetector according to some embodiments of the present disclosure,and FIG. 8C illustrates the one to one coupling between a substituentand a photodetector according to some embodiments of the presentdisclosure;

FIG. 9 is a block diagram illustrating the configuration of a processorof an imaging system according to some embodiments of the presentdisclosure;

FIG. 10 is a block diagram illustrating an image processing module of aprocessor according to some embodiments of the present disclosure;

FIG. 11 is a flowchart illustrating a process of image processingaccording to some embodiments of the present disclosure;

FIG. 12 is a flowchart illustrating another process of image processingaccording to some embodiments of the present disclosure.

FIG. 13 illustrates an exemplary configuration of scintillator crystalsin a sparse detector according to some embodiments of the presentdisclosure.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth by way of examples in order to provide a thorough understanding ofthe relevant disclosure. However, it should be apparent to those skilledin the art that the present disclosure may be practiced without suchdetails. In other instances, well known methods, procedures, systems,components, and/or circuitry have been described at a relativelyhigh-level, without detail, in order to avoid unnecessarily obscuringaspects of the present disclosure. Various modifications to thedisclosed embodiments will be readily apparent to those skilled in theart, and the general principles defined herein may be applied to otherembodiments and applications without departing from the spirit and scopeof the present disclosure. Thus, the present disclosure is not limitedto the embodiments shown, but to be accorded the widest scope consistentwith the claims.

It will be understood that the term “system,” “engine,” “unit,”“module,” and/or “block” used herein are one method to distinguishdifferent components, elements, parts, section or assembly of differentlevel in ascending order. However, the terms may be displaced by otherexpression if they may achieve the same purpose.

It will be understood that when a unit, engine, module or block isreferred to as being “on,” “connected to” or “coupled to” another unit,engine, module, or block, it may be directly on, connected or coupledto, or communicate with the other unit, engine, module, or block, or anintervening unit, engine, module, or block may be present, unless thecontext clearly indicates otherwise. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items.

The terminology used herein is for the purposes of describing particularexamples and embodiments only, and is not intended to be limiting. Asused herein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “include,”and/or “comprise,” when used in this disclosure, specify the presence ofintegers, devices, behaviors, stated features, steps, elements,operations, and/or components, but do not exclude the presence oraddition of one or more other integers, devices, behaviors, features,steps, elements, operations, components, and/or groups thereof.

This disclosure relates to an imaging technology, and more particularly,to a sparse detector imaging method and system. The system may include asparse detector including an array of scintillator crystals. In someembodiments, at least a portion of the scintillator crystals may bespaced apart according to a sparsity rule to form a sparse detectorarray. The configuration of the sparse detector array may be such thatthe amount of scintillator material used to build the detectors in thesystem may be reduced and that the system may be used to generate imagesof desirable quality.

FIG. 1 is an illustration of an imaging system according to someembodiments of the present disclosure. In some embodiments, the imagingsystem may be a single modality imaging system. The single modalityimaging system may include, for example, a Computed Tomography (CT)system, a Positron Emission Tomography (PET) system, a DigitalRadiography (DR) system, a Single Photon Emission Computed Tomography(SPECT) system, etc. In some embodiments, the imaging system may be amulti-modality imaging system. The multi-modality imaging system mayinclude, for example, a Computed Tomography-Positron Emission Tomography(CT-PET) system, a Computed Tomography-Magnetic Resonance Imaging(CT-MRI) system, a Positron Emission Tomography-Magnetic ResonanceImaging (PET-MRI) system, a Single Photon Emission ComputedTomography-Computed Tomography (SPECT-CT) system. The operatingmechanisms of different imaging modalities may be the same or differentaccording to some embodiments of the present disclosure. Accordingly,the imaging data acquired by different imaging modalities may also bethe same or different. Particularly, in some embodiments, the imagingdata of different modalities may complement one another, therebyproviding a set of imaging data describing a target from differentanalytical angles. For example, in some embodiments, the multi-modalityimaging may achieve the merging of morphological and functional images.The exemplary imaging systems described herein that may be used inconnection with the present system are not exhaustive and are notlimiting. Numerous other changes, substitutions, variations,alterations, and modifications may be ascertained to one skilled in theart and it is intended that the present disclosure encompass all suchchanges, substitutions, variations, alterations, and modifications asfalling within the scope of the present disclosure.

As illustrated in FIG. 1, the imaging system may include an imagingdevice 101, a processor 102, a terminal 103, a database 104, and anetwork 105. The imaging device 101 may be configured to examine atarget. In some embodiments, the imaging device 101 may include aplurality of imaging detectors. An imaging detector may include ascintillator and a photodetector. A plurality of imaging detectors mayform a sparse detector array.

The target that may be examined by the imaging device 101 may be anyorganic or inorganic mass, natural or man-made, that has a chemical,biochemical, biological, physiological, biophysical and/or physicalactivity or function. Merely by way of example, a target pertaining tothe present disclosure may include a cell, a tissue, an organ, a part ofor a whole body of a human or an animal. In some embodiments, the targetmay include a substance, a tissue, an organ, an object, a specimen, abody, or the like, or any combination thereof. In some embodiments, thesubject may include a head, a breast, a lung, a pleura, a mediastinum,an abdomen, a long intestine, a small intestine, a bladder, agallbladder, a triple warmer, a pelvic cavity, a backbone, extremities,a skeleton, a blood vessel, or the like, or any combination thereof.Other exemplary embodiments may include but not limited to man-madecomposition of organic and/or inorganic matters that are with or withoutlife. The exemplary targets described herein that may be examined inconnection with the present system are not exhaustive and are notlimiting. Numerous other changes, substitutions, variations,alterations, and modifications may be ascertained to one skilled in theart and it is intended that the present disclosure encompass all suchchanges, substitutions, variations, alterations, and modifications asfalling within the scope of the present disclosure.

In some embodiments, the imaging device 101 may include a gantry 510 (asshown in FIGS. 5A through 5C). The target 520 may be placed within thegantry 510 during imaging. In some embodiments, the imaging device 101may not include a gantry. Instead, the target may be placed in front ofthe imaging device 101. In some embodiments where the target may be ahuman patient, the human patient may take any suitable position duringimaging. Merely by way of examples, the human patient may lie on theback, lie in prone, sit, and stand within the gantry or in front of theimaging device 101.

The processor 102 may be configured to process imaging data. Theprocessor 102 may be configured to perform functions of image processingand imaging device 101 controlling. In some embodiments, the processor102 may be configured to perform operations including, for example, datapreprocessing, image reconstruction, image correction, or the like, or acombination thereof. In some embodiments, the processor 102 may beconfigured to generate a control signal relating to the configuration ofthe imaging device 101. In some embodiments, the processor 102 mayinclude any processor-based and/or microprocessor-based units. Merely byway of examples, the processor may include a microcontroller, a reducedinstruction set computer (RISC), application specific integratedcircuits (ASICs), an application-specific instruction-set processor(ASIP), a central processing unit (CPU), a graphics processing unit(GPU), a physics processing unit (PPU), a microcontroller unit, adigital signal processor (DSP), a field programmable gate array (FPGA),an acorn reduced instruction set computing (RISC) machine (ARM), or anyother circuit or processor capable of executing the functions describedherein, or the like, or any combination thereof. In some embodiments,the processor 102 may also include a memory. In some embodiments, thememory may include Random Access Memory (RAM). In some embodiments, thememory may include Read Only Memory (ROM). The processor that may beused in connection with the present system described herein are notexhaustive and are not limiting. Numerous other changes, substitutions,variations, alterations, and modifications may be ascertained to oneskilled in the art and it is intended that the present disclosureencompass all such changes, substitutions, variations, alterations, andmodifications as falling within the scope of the present disclosure.

The terminal 103 may be configured to receive input and/or displayoutput. The terminal 103 may be configured to communicate with theprocessor 102 and allow one or more operators to control the productionand/or display of images. The terminal 103 may include, for example, adisplay, a mobile device (e.g., a smart phone, a tablet, a laptopcomputer, or the like), a personal computer, other devices, or the like,or a combination thereof. Other devices may include a device that maywork independently, or a processing unit or processing module assembledin another device (e.g., an intelligent home terminal). The terminal 103may be configured to receive input. The terminal 103 may include aninput device, a control panel (not shown in the figure), etc. The inputdevice may be a keyboard, a touch screen, a mouse, a remote controller,or the like, or any combination thereof. An input device may includealphanumeric and other keys that may be inputted via a keyboard, a touchscreen (for example, with haptics or tactile feedback), a speech input,an eye tracking input, a brain monitoring system, or any othercomparable input mechanism. The input information received through theinput device may be communicated to the processor 102 via, for example,a bus, for further processing. Another type of the input device mayinclude a cursor control device, such as a mouse, a trackball, or cursordirection keys to communicate direction information and commandselections to, for example, the processor 102 and to control cursormovement on the display device. The terminal 103 may be configured todisplay output. Exemplary information may include, for example, animage, a request for input or parameter relating to image acquisitionand/or processing, or the like, or a combination thereof. The displaydevice may include a liquid crystal display (LCD), a light emittingdiode (LED)-based display, a flat panel display or curved screen (ortelevision), a cathode ray tube (CRT), or the like, or a combinationthereof.

The database 104 may be configured to store data. The data to be storedmay be from the imaging device 101, the processor 102, the terminal 103,the database 104, and/or the network 105. Exemplary data that may bestored may include imaging data acquired by the imaging device 101, asparsity rule, a lookup table, the efficiency of a virtual scintillatorunit, the efficiency of the line of response, a reconstructed image,etc. In some embodiments, the database 104 may be a hard disk drive. Insome embodiments, the database 104 may be a solid-state drive. In someembodiments, the database 104 may be a removable storage drive. Merelyby way of examples, a non-exclusive list of removable storage drive thatmay be used in connection with the present disclosure includes a flashmemory disk drive, an optical disk drive, or the like, or a combinationthereof.

In some embodiments, the imaging device 101, the processor 102, theterminal 103, and the database 104 may be connected to or communicatewith each other directly. In some embodiments, the imaging device 101,the processor 102, the terminal 103, the database 104 may be connectedto or communicate with each other via the network 105. The network 105may be wired or wireless. The wired connection may include using a metalcable, an optical cable, a hybrid cable, an interface, or the like, orany combination thereof. The wireless connection may include using aLocal Area Network (LAN), a Wide Area Network (WAN), a Bluetooth, aZigBee, a Near Field Communication (NFC), or the like, or anycombination thereof. The network that may be used in connection with thepresent system described herein are not exhaustive and are not limiting.Numerous other changes, substitutions, variations, alterations, andmodifications may be ascertained to one skilled in the art and it isintended that the present disclosure encompass all such changes,substitutions, variations, alterations, and modifications as fallingwithin the scope of the present disclosure.

It should be noted that the imaging system described above is providedfor the purposes of illustration, and not intended to limit the scope ofthe present disclosure. Apparently for persons having ordinary skills inthe art, numerous variations and modifications may be conducted underthe teaching of the present disclosure. However, those variations andmodifications may not depart the protecting scope of the presentdisclosure.

FIG. 2 is a flowchart illustrating a process for an imaging methodaccording to some embodiments of the present disclosure. Prior toacquiring imaging data of a target or a portion of a target, the imagingdevice 101 and/or target may be adjusted to obtain the most advantageousanalysis position or angle. The positioning of imaging device 101 and/orthe target may be accomplished manually and/or automatically.

As illustrated in step 201, the imaging data of a target may beacquired. The acquisition may be accomplished by the imaging device 101.The imaging device 101 may detect the radiation released from the targetand convert the radiation signal into electrical signal. The electricalsignal may be further converted to computer-readable signal.

In step 202, the acquired imaging data may be processed. The dataprocessing may include image reconstruction, image correction, and dataestimation. The data processing may be executed by the processor 102. Insome embodiments, data processing may be performed in parallel to, or,as needed, after all imaging data have been acquired.

In step 203, the system may output the processed imaging data. Theoutput step may be performed by the terminal 103. Merely by way ofexamples, the processed imaging data may be delivered to a display,printer, computer network, or other device. The output imaging data mayalso comprise two-dimensional (2D) images, a three-dimensional (3D)volume, or a 3D volume over time (4D).

In step 204, the data generated during step 201, step 202, and step 203may be stored. Exemplary data that may be stored may include imagingdata acquired by the imaging device 101, a pattern of the sparsedetectors, a sparsity rule, a lookup table, the efficiency of a virtualscintillator unit, the efficiency of the line of response, reconstructedimage, etc. The data may be stored in the database 104. In someembodiments, the method to store may include sequential storage, linkstorage, hash storage, index storage, or the like, or any combinationthereof.

It should be noted that the flowchart described above is provided forthe purposes of illustration, and not intended to limit the scope of thepresent disclosure. Apparently for persons having ordinary skills in theart, numerous variations and modifications may be conducted under theteaching of the present disclosure. However, those variations andmodifications may not depart the protecting scope of the presentdisclosure.

FIG. 3 is a block diagram illustrating the configuration of an imagingdevice according to some embodiments of the present disclosure. Animaging device 101 may include an apparatus 301 and a signal processor302. It should be noted that the imaging device 101 may include othermodules or units such as a gantry, a patient table, a high-voltage tank.In some embodiments, the imaging device 101 may further include aradiation generating unit which may be configured to emit radiation insome system, e.g., a CT system, a DR system, a CT-PET system. Theradiation generating unit may be a cold cathode ion tube, a high vacuumhot cathode tube, a rotating anode tube, etc.

The apparatus 301 may refer to a device for detecting radiation andprovide an output according to the detected radiation. The radiationused herein may include a particle ray, a photon ray, or the like, or acombination thereof. The particle ray may include neutron, proton,electron, pt-meson, heavy ion, or the like, or any combination thereof.The photon ray may include X-ray, γ-ray, α-ray, β-ray, ultraviolet,laser, or the like, or any combination thereof. In some embodiments, theradiation received by the apparatus 301 may come directly from theradiation generating unit or other radiation source. In someembodiments, the radiation received by the apparatus 301 may be theradiation emitted from the target under examination or the radiationtraversing the target under examination. For example, in a CT system,the detector may detect the radiation from an X-ray tube and traversingthe target under examination. Another example in a PET system, thegamma-ray emitted from the target under examination may be received bythe apparatus 301.

In some embodiments of the present disclosure, the apparatus 301 mayinclude one or more detectors. In some embodiments, the apparatus 301may be a one-dimensional apparatus, a two-dimensional apparatus, athree-dimensional apparatus, etc. The apparatus 301 may assume differentconfigurations. Details regarding the configuration of the apparatus 301will be further explained in FIGS. 5A through 5C. The numbers of thecolumn and row of detectors in one apparatus may be varied according tothe different demands, e.g., image resolution, the whole size of thedetector and pixel, cost, or the like. In some embodiments, thedetectors may be arranged in a uniform pattern or a non-uniform pattern.For example, the detectors may be arranged to form an angle, which maybe arbitrary.

The detector in the apparatus 301 may include a scintillator and aphotodetector. The scintillator may include an array of scintillatorcrystals. The photodetector may include an array of photodetectorelements. The scintillator crystals and the photodetector elements maybe coupled directly and indirectly. As used herein, coupling mayindicate that the optical signal produced in a scintillator crystal or ascintillator may be transmitted to a photodetector or a photodetectorelement. Details regarding the coupling between the scintillatorcrystals and the photodetector elements will be further explained inFIGS. 6 through 7. The scintillator crystals in the detector 310 may bearranged tightly or sparsely. The sparsity may be between 1% and 50%, orbetween 2% and 45%, or between 3% and 40%, or between 4% and 35%, orbetween 5% and 30%, or below 60%, or below 50%, or below 40%, or below30%, or below 20%. Merely by way of example, the sparsity may beapproximately 10%, or 15%, or 20%, or 25%, or 30%, or 35%, or 40%. Thesparsity of each detector may be the same or different. Detailsregarding the sparseness of the detector will be further explained inFIG. 8.

The scintillator crystal may include any material that has the abilityto absorb ionizing radiation and to emit a fraction of the absorbedenergy as light. Provided below is a non-exhaustive list of exemplaryembodiments of suitable scintillator materials: CdWO4, BaF₂, CsF,CsI(Na), CsI(Tl), NaI(Tl), CaF₂(Eu), lutetium oxyorthosilicate (LSO)crystals; bismuth germinate (BGO) crystals, gadolinium oxyorthosilicate(GSO) crystals, LYSO crystals, and mixed lutetium silicates (MLS)crystals. The size of the scintillator crystal may vary according to oneor more conditions including, for example, image resolution,sensitivity, stability, the size of the detector or the like, or anycombination thereof. The size of the scintillator crystals in thedetector may be the same or various. Merely by way of example, thelength and/or width of the scintillator may range from severalmicrometers to several hundred micrometers. For instance, the height ofthe scintillator may range from several micrometers to several hundredmicrometers, e.g., 500 micrometers. The shape of the cross-section of ascintillator crystal may be circular, oval, rectangular, or the like, orany combination thereof. As used herein, the long axis of a scintillatorcrystal is the direction perpendicular to the base to which thescintillator crystal is attached when it is packaged into a detector. Across-section of a scintillator crystal is a plane within thescintillator crystal that is perpendicular to the long axis thereof.

The photodetector element may be a photoelectric conversion element. Aphotoelectric conversion element may firstly detect an optical signaland then may convert the optical signal into an electrical signalincluding, e.g., electrical current, electrical voltage, and/or otherelectrical phenomena. The photodetector element in some embodiments ofthe present disclosure may include a phototube, a Photomultiplier Tube(PMT), a photodiode, an active-pixel sensor, a bolometer, a CCD, agaseous ionization detector, a photoresistor, a phototransistor,Avalanche Photodiode (APD), Single-Photon Avalanche Photodiode (SPAD),Silicon Photomultiplier (SiPM), Digital Silicon Photomultiplier (DSiPM),or the like, or any combination thereof. The size of the photodetectorelement may vary based on one or more conditions including, for example,image resolution, sensitivity, stability, the size of the scintillator,the size of the scintillator crystal, or the like, or any combinationthereof. Merely by way of example, the length and/or width of thephotodetector element may range from several micrometers to severalhundred micrometers. Merely by way of example, the height of thephotodetector may range from several micrometers to several hundredmicrometers, e.g., 500 micrometers. The cross-section of a photodetectorelement may be circular, oval, rectangular, or the like, or anycombination thereof. The photodetector element may be arrangedregularly, or irregularly. As used herein, the long axis of aphotodetector element is the direction perpendicular to the base towhich the photodetector element is attached when it is packaged into adetector. A cross-section of a photodetector element is a plane withinthe photodetector element that is perpendicular to the long axisthereof.

It should be noted that the above description about the detector ismerely an example according to the present disclosure. Obviously, tothose skilled in the art, after understanding the basic principles ofthe detector, the form and details of the detector may be modified orvaried without departing from the principles. The modifications andvariations are still within the scope of the current disclosuredescribed above. For example, the number of detector in the apparatusmay be one, two, three, or any number based on the actual demand. Insome embodiments, the radiation generating unit may include severalX-ray tubes.

The signal processor 302 of the imaging device 101 may be configured toconvert the radiation received by the apparatus 301 to imaging data. Theterm “imaging data” used herein may refer to the data based on signalsdetected by the detectors and used to reconstruct an image. The signalprocessor 302 may generate some imaging data based on the output fromthe photodetector elements. In some embodiments, the signal processor302 may measure the time that radiation may be received by the apparatus301, calculate the radiation energy received by the apparatus 301, anddetermine the position of the radiation traversing the target underexamination, or the like, or any combination thereof.

For example, in a PET system, when a PET tracer molecule is introducedinto the target, positrons may be emitted by the PET tracer molecule.After moving a distance, e.g., 1 micrometer, the positrons may undergoannihilations with the electrons and electron-positron annihilations mayresult in two 511 keV gamma photons, which upon their own generation,begin to travel in opposite directions with respect to one another. Thisprocess may be referred as a coincidence event. A coincidence event isassigned to a line of response (LOR) joining the two relevant detectors.Because of the different trajectories of the two gamma photons, the timethat the gamma photons are detected by the detectors may be different.The signal processor 302 may measure the difference of the time a pairof gamma photons received by the two relevant detectors respectively,determine the position of annihilation, calculate the radiation energyreceived by the two relevant detector, and calculate the number ofcoincidence events. The signal processor 302 may perform the processmentioned above based on the signals from the photodetector.

It should be noted that the above description about the signal processoris merely an example according to the present disclosure. Obviously, tothose skilled in the art, after understanding the basic principles ofthe signal processor, the form and details of the signal processor maybe modified or varied without departing from the principles. Themodifications and variations are still within the scope of the currentdisclosure described above. For example, the signal processor mayamplify, digitize, and/or analyze the signal from the photodetectorbefore measuring the detection time, calculating the position,calculating the energy and/or counting the number.

FIG. 4 is a flowchart illustrating a process for obtaining imaging dataof an imaging device according to some embodiments of the presentdisclosure. It should be noted that process described below is merelyprovided for illustrating an example of the radiation imaging, and notintended to limit the scope of the present disclosure. The radiationused herein may include a particle ray, a photon ray, or the like, or acombination thereof. The particle ray may include neutron, proton,electron, μ-meson, heavy ion, or the like, or any combination thereof.The photon beam may include X-ray, γ-ray, α-ray, β-ray, ultraviolet,laser, or the like, or any combination thereof.

As illustrated in FIG. 4, in step 401, light signals are obtained. Thisprocess may be performed by the scintillator or other components thatmay sense radiation and convert it to light. Before this step, theradiation may be generated. In some embodiments, the radiation may comefrom a radiation generating unit such as an X-ray tube. In someembodiments, the radiation may be generated by electron-positronannihilation. The positrons may be emitted by tracer moleculesintroduced into a target. After the radiation is generated, theradiation may be converted into the form of visible or invisible light.

The light signals may then be converted into electrical signals in step402. This step may be performed by the photodetectors in the apparatus301. The photodetectors may sense the light signals emitted from thescintillator and convert them into corresponding electrical signals.Exemplary embodiments of a photodetector element that may be used inconnection with the present system include Photomultiplier Tube (PMT),Avalanche Photodiode (APD), Single-Photon Avalanche Photodiode (SPAD),Silicon Photomultiplier (SiPM), Digital Silicon Photomultiplier (DSiPM).The exemplary photodetectors described herein that may be used inconnection with the present system described above are not exhaustiveand are not limiting; numerous other changes, substitutions, variations,alterations, and modifications may be ascertained to one skilled in theart and it is intended that the present disclosure encompass all suchchanges, substitutions, variations, alterations, and modifications asfalling within the scope of the present disclosure.

The obtained electrical signals may be processed in step 403. This stepmay be performed by the signal processor 302 or other modules or unitsin the system. In some embodiments, based on the electrical signals, thesignal processor 302 may record the time radiation was detected, assessthe radiation energy, assess the amount of the radiation received by theapparatus 301, determine the position of the radiation traversing thetarget under examination, or the like, or any combination thereof. Insome embodiments, the signal processor 302 may calculate the number ofcoincidence events. Besides, the signal processor 302 may amplify,digitize, and/or analyze the signal from a photodetector.

After the electrical signals are processed, imaging data may be obtainedin step 404. The imaging data may be used to reconstruct an image of thetarget under examination. Image reconstruction may be performed by othercomponents of the imaging system, or by an image processing device orsystem outside of the imaging system.

It should be noted that the above description about the process ofobtaining imaging data is merely an example according to the presentdisclosure. Obviously, to those skilled in the art, after understandingthe basic principles of the process of obtaining imaging data, the formand details of the process may be modified or varied without departingfrom the principles. In some embodiments, other steps may added in theprocess. For example, the intermediated data and/or the final data ofthe process may be stored in the process. The modifications andvariations are still within the scope of the current disclosuredescribed above.

FIGS. 5A through 5C illustrate different configurations that theapparatus 301 may assume according to some embodiments of the presentdisclosure. FIGS. 5A through 5C illustrate a position relationship ofthe apparatus 301, a gantry 510, and a target 520. The apparatus mayinclude a plurality of detector modules 501 as shown in the figures. Insome embodiments, the apparatus may include two or more plurality ofdetector modules 501. A detector module 501 may include one or moredetectors. The gantry 510 may have a circular cross-section as shown inFIGS. 5A through 5C. In some embodiments, the gantry 510 may have across-section of any other shapes suitable for imaging. Merely by way ofexamples, the gantry 510 may have a rectangular cross-section, anelliptical cross-section, a polygonal cross-section, etc. The gantry 510may have cross-sections of various shape and/or size along the directionperpendicular to the cross-sections. A target 520 to be examined may beplaced in the gantry 510. In some embodiments, the detector modules 501may be positioned circumferentially around the gantry 510. In someembodiments, the detector modules 501 may not be positioned around thegantry 510 but right next to the target 520. In some embodiments, thedetector modules 501 may be fixed on a patient table (not shown in thefigure). In some embodiments, the detector modules 501 may be stationaryduring imaging. In some embodiments, the detector modules 501 may becircumferentially movable around the target 520. In some embodiments,one of the detector modules 501 may be independently movable withrespect to another detector module 501.

As shown in FIG. 5A, the apparatus 301 may include two detector modules501. The side of scintillators of one detector module may face or opposethe side of scintillators of the other detector module. In someembodiments, the two detector modules 501 may be parallel to each other.In some embodiments, the two detector modules 501 may be at an angle(for example, an oblique angle or a right angle) with to each other. Insome embodiments, the two detector modules 501 may be positionedsymmetrically about the center of the gantry 510. In some embodiments,the two detector modules 501 may be positioned asymmetrically about thecenter of the gantry 501.

FIG. 5B illustrates another configuration of the apparatus 301 accordingto some embodiments of the present disclosure. As shown in FIG. 5B, theapparatus 301 may include four detector modules 501. In someembodiments, the angle between neighboring detector modules 501 may beapproximately 90 degrees. The four detector modules 501 may surround agantry 510. A target 520 may be placed within the gantry. In someembodiments, the four detector modules may not surround a gantry 510 butbe positioned right next to the target 520. The sides of scintillatorsof the detector modules 501 may face the target 520. Two detectiondetector modules 501 may form a pair. The sides of the scintillators ofthe pair of detector modules 501 may face each other.

FIG. 5C illustrates another configuration of the apparatus 301 accordingto some embodiments of the present disclosure. As shown in FIG. 5C, theapparatus 301 may include eight detector modules 501. In someembodiments, the eight detector modules 501 may substantially form anoctagon. The eight detector modules 501 may distribute evenly with eachdetector module 501 facing a separate octant of a 360-degree field. Thesides of scintillators of the detector modules 501 may face the target520. Two detection detector modules 501 may form a pair. The sides ofthe scintillators of the pair of detector modules 501 may face eachother.

FIG. 5D illustrates another configuration of the apparatus 301 accordingto some embodiments of the present disclosure. As shown in FIG. 5D, theapparatus 301 may include a plurality of detectors forming a ring. Thering formed by the plurality of detector modules may be concentric withrespect to the gantry 510. The sides of scintillators of the detectormodules in the ring may face the target 520. The sides of scintillatorsof the detector modules opposing each other may face each other.

It should be noted that the configurations of detectors described aboveis provided for the purposes of illustration, and not intended to limitthe scope of the present disclosure. Apparently for persons havingordinary skills in the art, numerous variations and modifications may beconducted under the teaching of the present disclosure. However, thosevariations and modifications may not depart the protecting scope of thepresent disclosure.

In some embodiments, a detector module 501 may include a sparsedetector. A sparse detector may refer to a detector having at least aportion of scintillator crystals spaced apart based on a sparsity rule.

FIGS. 6A and 6 B illustrate a non-sparse detector and a sparse detectoraccording to some embodiments of the present disclosure, respectively.As shown in FIG. 6A, the scintillator 610 in a non-sparse detector mayinclude an array of scintillator crystals 601 packed together and notspaced apart.

FIG. 6B illustrates a scintillator 620 of a sparse detector. As shown inFIG. 6B, the scintillator 620 may include scintillator crystals 601 andsubstituents or gaps 602. In some embodiments, at least a portion of thescintillator crystals 601 may be spaced apart by the substituents orgaps 602. In some embodiments, at least a portion of the scintillatorcrystals 601 may be spaced apart by the substituents 602. In someembodiments, at least a portion of the scintillator crystals 601 may bespaced apart by gaps 602. In some embodiments, the sparse detector mayinclude both substituents and gaps, and at least a portion of thescintillator crystals 601 may be spaced apart by either the substituentsor the gaps 602.

The substituent 602 may be a light-transmitting material. Thesubstituent 602 may be in the solid state, the liquid state, or the gasstate. Merely by way of examples, the substituent 602 may be glass, air,or one or more other materials. In some embodiments, one substituent 602may occupy the same volume as one scintillator crystal. The ratio of thevolume of said substituents to the volume of a scintillator may be up to60%, or up to 50%, or up to 40%, or up to 30%, or up to 25%, or up to20%, or up to 15%, or up to 10%, or up to 8%, or up to 5%. In someembodiments of the present disclosure, the space between the sidewallsof neighboring scintillator crystals in a scintillator 620 may be filledwith a reflective material to increase the internal reflection along thesidewalls of the crystals, while decreasing the crosstalk between theneighboring crystals. As used herein, a sidewall of a scintillatorcrystal may refer to a wall forming the side of the scintillator crystalthat may be parallel or substantially parallel to the long axis of thescintillator crystal.

The sparsity of the sparse detector 620 may follow a sparsity rule. Insome embodiments, the sparsity rule may designate a way of creating asparse detector by substituting one or more scintillator crystals in anon-sparse detector with substituents or gaps.

Merely by way of examples, a sparsity rule for a sparse detector, asopposed to a non-sparse detector, may be to group scintillator crystalsof a non-sparse detector into subsets containing a first number ofscintillator crystals, and in one or more subsets, to substitute one ormore scintillator crystals with one or more substituents or gaps. Thesubsets of scintillator crystals may include an equal, or a variousfirst numbers of scintillator crystals. For example, a subset ofscintillator crystals may include two, three, four, five, or any numberof scintillator crystals. The scintillator crystals in a subset may beneighboring, partially neighboring, or completely surrounded bysubstituents or gaps. In some embodiments, every scintillator crystal ofthe subset is next to at least one scintillator crystal of the subset.In some embodiments, at least two of the scintillator crystals in asubset are next to each other; at least two of the scintillator crystalsin a subset are spaced apart by a substituent or gap. In someembodiments, a subset of scintillator crystals containing at leastpartially neighboring scintillator crystals may exhibit a geometricpattern. For example, in some embodiments, a subset of scintillatorcrystals may include four at least partially neighboring scintillatorcrystals positioned in one direction (for example, along a line, etc.),scintillator crystals positioned in two directions(for example,exhibiting an L-shape, a square, a T-shape, a rectangle, etc.).

The subsets of scintillator crystals may be spaced according to a samesparsity rule or a different sparsity rule. The sparsity rule mayinclude the number of substituent(s) in a subset (i.e. the secondnumber), the position(s) of the substituent(s) relative to theposition(s) of the scintillator crystal(s) in the subset, the number ofscintillator crystal(s) in the subset (i.e. the first number), or thelike, or a combination thereof. For example, the second number ofscintillator crystals in a subset may be zero, one, two, three, or anynumber smaller than, or equal to the first number of scintillatorcrystals in the subset. In some embodiments, the sparseness of a subset,i.e., the ratio of the second number of substituents or gaps in a subsetto the first number of scintillator crystals in a subset, may be between1% to 50%, or between 2% and 45%, or between 3% and 40%, or between 4%and 35%, or between 5% and 30%, or below 60%, or below 50%, or below40%, or below 30%, or below 20%. The sparseness of each subset may beequal or various. In some embodiments, the overall sparseness of thesparse detector may be between 1% to 50%, or between 2% and 45%, orbetween 3% and 40%, or between 4% and 35%, or between 5% and 30%, orbelow 60%, or below 50%, or below 40%, or below 30%, or below 20%.

Merely by way of examples, possible sparsity rules that may be used inconnection with some embodiments of the present disclosure may include:to substitute at most one scintillator crystal out of a subset of twoneighboring scintillator crystals with a substituent or a gap, tosubstitute no more than one scintillator crystal out of a subset ofthree neighboring scintillator crystals with a substituent or a gap, tosubstitute no more than two scintillator crystals out of a subset offive neighboring scintillator crystals with a substituent or a gap, orthe like, or any combination thereof. For example, a sparsity rule mayinclude two types of subsets of scintillator crystals containing two andthree scintillator crystals in each subset, respectively, and at mostone scintillator crystal out of a subset of two neighboring scintillatorcrystals with a substituent or a gap, no more than one scintillatorcrystal out of a subset of three neighboring scintillator crystals witha substituent or a gap. It is understood that the description is forillustrating exemplary structures, configurations, or scintillatorcrystal layout of a sparse detector as opposed to a non-sparse detector,and is not intended to illustrate or suggest a way of manufacturing asparse detector. For instance, the description of “to substitute at mostone scintillator crystal out of two neighboring scintillator crystalswith a substituent or a gap” does not suggest that to form a sparsedetector, a non-sparse detector is formed, and some scintillatorcrystals are removed from the non-sparse detector to make room forsubstituents or gaps.

In some embodiments, the sparse detector may exhibit a periodic patternof scintillator crystals being spaced apart. As used herein, the term“periodic pattern” may refer to that a periodic unit including thegeometric pattern exhibited by each subset of scintillator crystals andthe substituents or gaps between the scintillator crystals repeats in asparse detector. A periodic unit may include one or more subsets.

Merely by way of example, in some embodiments, a sparse detector mayfollow a sparsity rule to substitute one scintillator crystals in asubset of two neighboring scintillator crystals, and the one substitutedscintillator crystals may occupy the same relative position of the twoneighboring scintillator crystals (for example, imagine that a column ofscintillator crystals along the circumferential direction of a gantry istaken and spread out as a rectangle in front of us, and we are lookingfrom left to right, the left one or the right one of the two neighboringscintillator crystals in a subset is always substituted). In thisexample, the periodic unit may include a subset of two neighboringscintillator crystals and the one substituted scintillator crystalspositioned as described above. A sparse detector exhibiting such apattern may be referred to as exhibiting a periodic pattern.

As another example, in some embodiments, a sparse detector followingmore than sparsity rules may exhibit a periodic pattern as well. Forexample, in some embodiments, a sparse detector may follow a sparsityrule to substitute at most one scintillator crystals in a subset of twoneighboring scintillator crystals. A subset in such occasions mayexhibit three geometric patterns, e.g., pattern one of non-substitution,pattern two of the left one of the subset of two scintillator crystalsbeing substituted, and pattern three of the right one of the subset oftwo scintillator crystals being substituted. The three pattern may allexist in a sparse detector. In some embodiments, the three patterns mayform a periodicity following a certain order. In further detail, thefirst subset may exhibit pattern one, the second subset may exhibitpattern two to the right of the first subset, the third subset mayexhibit pattern three to the right of the second subset, the fourthsubset may exhibit pattern one again, the fifth subset may exhibitpattern two to the right of the fourth subset, the sixth subset mayexhibit pattern three to the right of the fifth subset, and so forth. Inthis example, a periodic unit may include three subsets, the firstsubset exhibiting pattern one, the second subset may exhibiting patterntwo positioned to the right of the first subset, and the third subsetexhibiting pattern three positioned to the right of the second subset.

A sparse detector may include a plurality of periodic units. A periodicunit may include at least 10 scintillator crystals, or at least 20scintillator crystals, or at least 30 scintillator crystals, or at least40 scintillator crystals, or at least 50 scintillator crystals, or atleast 60 scintillator crystals, or at least 70 scintillator crystals, orat least 80 scintillator crystals, or at least 90 scintillator crystals,or at least 100 scintillator crystals. A periodic unit may include atleast 10 substituents or gaps, or at least 20 substituents or gaps, orat least 30 substituents or gaps, or at least 40 substituents or gaps,or at least 50 substituents or gaps, or at least 60 substituents orgaps, or at least 70 substituents or gaps, or at least 80 substituentsor gaps, or at least 90 substituents or gaps, or at least 100substituents or gaps. In a periodic unit, the scintillator crystals arespaced apart by the substituents or gaps according to one or moresparsity rules.

It is understood that the periodic order described above is merely anexample and is not intended to limit, the subsets exhibiting patternsmay follow any possible orders applicable. In some embodiments, thefirst group of subsets may exhibit pattern one, the second group ofsubsets may exhibit pattern two, the third group of subsets may exhibitpattern three, the fourth group of subsets may exhibit pattern oneagain, and so forth. A group of subsets may include any number ofsubsets of scintillator crystals, such as five, ten, twenty, fifty, anda hundred.

In some embodiments, the sparse detector may exhibit a random pattern ofscintillator crystals being spaced apart. By “random pattern” usedherein it may refer to that the subsets of the scintillator crystalsexhibit no periodic geometric pattern or no period units. Using theexamples described in the previous paragraph that a sparse detectorfollows a sparsity rule that to substitute at most one scintillatorcrystals of a subset of two neighboring scintillator crystals. In such asubset, none or one scintillator crystals may be substituted bysubstituents or gaps. The substituted scintillator crystals may be anyone of the two neighboring scintillator crystals. In such occasion, asubset of two neighboring scintillator crystals may exhibit threepossible geometric pattern. The three patterns may not be periodic. Theoverall the sparse detector may exhibit a random pattern of scintillatorcrystals being spaced apart.

The sparse detector that may be used in connection with the presentsystem described herein are not exhaustive and are not limiting.Numerous other changes, substitutions, variations, alterations, andmodifications may be ascertained to one skilled in the art and it isintended that the present disclosure encompass all such changes,substitutions, variations, alterations, and modifications as fallingwithin the scope of the present disclosure.

FIG. 7A illustrates the indirect coupling between the scintillator andthe photodetector via the light guide according to some embodiments ofthe present disclosure. The scintillator and photodetector asillustrated may form a sparse detector. In some embodiments, thescintillator 701 may include an array of scintillator crystals 601 andsubstituents or gaps 602 between the scintillator crystals of the array.The scintillator crystals 601 may be spaced apart by the substituents orgaps 602. The distribution of the substituents or gaps 602 may beaccording to a sparsity rule.

The photodetector 702 may include an array of photodetector elements703. In some embodiments, the number of the photodetector elements 703on the photodetector 702 may be equal to the number of scintillatorcrystals 601 and substituents or gaps 602 on the scintillator 701. Insuch embodiments, the scintillator crystals 601 and substituents or gaps602 may be coupled to the photodetector elements 703 in a one-to-onepattern. In some embodiments, the number of photodetector elements 703on the photodetector 702 may be unequal to the number of scintillatorcrystals 601 and substituents or gaps 602 on the scintillator 701. Insuch embodiments, multiple scintillator crystals 601 and/or substituentsor gaps 602 may be coupled to a photodetector element 703. Merely by wayof examples, four of the scintillator crystals 601 and substituents orgaps 602 may be coupled to one photodetector element 703. In someembodiments, the number of photodetector elements 703 on thephotodetector 702 may be equal to the number of scintillator crystals601 on the scintillator 701. In such embodiments, one scintillatorcrystal 601 may be coupled to one photodetector element 703, and asubstituent or gap 602 may be not coupled to a photodetector element703.

A light guide 704 may be used to transmit the light coming out from thescintillator 701 to the photodetector 702. The light guide 704 mayspread the light signals (or referred to as optical signals) outputtedby a single scintillator crystal within the array of scintillatorcrystals such that it may be detected by at least one photodetectorelement. In some embodiments, the light guide 704 may include a lighttransmitting intermediate, e.g., an optical fiber, an optical fiberbundle, an optical glue, an optically coupling material, an immersionoil, or the like, or a combination thereof. In some embodiments, thescintillator 701 may be optically coupled to the photodetector 702 viaone or more optical fibers or optical fiber bundles. One end of theoptical fiber may be attached to the output end of the scintillator 701,and the other end of the optical fiber may be attached to the input endof the photodetector 702. In various embodiments, an optical fiberbundle may assume various configurations with respect to, for example,length, width, etc.

FIG. 7B illustrates the direct coupling between the scintillator 701 andthe photodetector 702 according to some embodiments of the presentdisclosure. The scintillator 701 and the photodetector 702 asillustrated may form a sparse detector. In some embodiments, thescintillator 701 may include an array of scintillator crystals 601 andsubstituents or gaps 602 between the scintillator crystals 601 of thearray. The scintillator crystals 601 may be spaced apart by thesubstituents or gaps 602. The distribution of the substituents or gaps602 may be according to a sparsity rule.

The photodetector 702 may include an array of photodetector elements703. In some embodiments, the number of the photodetector elements 703on the photodetector 702 may be equal to the number of scintillatorcrystals 601 and substituents or gaps 602 on the scintillator 701. Insuch embodiments, the scintillator crystals 601 and substituents or gaps602 may be coupled to the photodetector element 703 in a one-to-onepattern. In some embodiments, the number of photodetector elements 703on the photodetector 702 may be unequal to the number of scintillatorcrystals 601 and substituents or gaps 602 on the scintillator 701. Insuch embodiments, multiple scintillator crystals 601 and/or substituentsor gaps 602 may be coupled to a photodetector element 703. Merely by wayof examples, four of the scintillator crystals 601 and substituents orgaps 602 may be coupled to one photodetector element 703. In someembodiments, the number of photodetector elements 703 on thephotodetector 702 may be unequal to the number of scintillator crystals601 and substituents or gaps 602 on the scintillator 601. In suchembodiments, a portion of scintillator crystal 601 may be coupled to onephotodetector element 703, and a portion of substituent or gap 602 maybe not coupled to photodetector element 703. Merely by way of examples,one scintillator crystal 601 may be coupled to one photodetector element703, while the substituents or gaps 602 may be uncoupled tophotodetector elements 703.

A light guide may be unnecessary. As shown in FIG. 7B, the scintillator701 may be directly coupled to the photodetector 702 without the use ofa light guide. Particularly, the output end of the scintillator 701 maybe directly coupled to the input end of the photodetector 702.

It should be noted that the coupling between the scintillator and thephotodetector described above is provided for the purposes ofillustration, and not intended to limit the scope of the presentdisclosure. Apparently for persons having ordinary skills in the art,numerous variations and modifications may be conducted under theteaching of the present disclosure. However, those variations andmodifications may not depart the protecting scope of the presentdisclosure.

FIG. 8A illustrates the one-to-one coupling between the scintillator andthe photodetector according to some embodiments of the presentdisclosure. The scintillator and the photodetector as illustrated mayform a sparse detector. In some embodiments, the scintillator 701 mayinclude an array of scintillator crystals 601 and substituents or gaps602 between the scintillator crystals of the array. The scintillatorcrystals 601 may be spaced apart by the substituents or gaps 602. Thedistribution of the substituents or gaps 602 may be according to asparsity rule.

In some embodiments, the scintillator 701 may be directly coupled to thephotodetector 702. For instance, the output end of the scintillator 701may be directly coupled to the input end of the photodetector 702. Insome embodiments, the scintillator 701 and the photodetector 702 may beindirectly coupled via a light transmitting intermediate including, forexample, an optical fiber, an optical fiber bundle, an optical glue, anoptically coupling material, an immersion oil, or the like, or acombination thereof.

FIG. 8B illustrates a one-to-one coupling between a scintillator crystal601 and a photodetector element 703 according to some embodiments of thepresent disclosure. As used herein, a one-to-one coupling between ascintillator crystal and a photodetector element may indicate that theoptical signal detected in a scintillator crystal may be transmitted toa photodetector element. In some embodiments, the output end of ascintillator crystal 601 may be directly coupled to the input end of aphotodetector element 703. In some embodiments, the output end of ascintillator crystal 601 of the scintillator 701 may be indirectlycoupled to the input end of a photodetector element 703 of thephotodetector 702 via, for example, a light transmitting intermediate.

FIG. 8C illustrates the one-to-one coupling between a substituent and aphotodetector element according to some embodiments of the presentdisclosure. In some embodiments, one end of a substituent 602 may bedirectly coupled to the input end of a photodetector element 703. Insome embodiments, one end of the substituent 602 may be indirectlycoupled to the input end of the photodetector element 703 via a lighttransmitting intermediate.

Various embodiments of the present disclosure may include other ways ofcoupling between the scintillator of a sparse detector and thephotodetector. For example, in some embodiments, the photodetector mayhave a sparse configuration as well. The photodetector may includesubstituents or gaps among the photodetector elements, and thephotodetector elements may be spaced apart by the substituents or gaps.In some embodiments, the photodetector elements may be spaced apartaccording to a sparsity rule. In some embodiments, the photodetectorelements and the scintillator may share a same pattern. In suchembodiments, one scintillator crystal of the scintillator may be coupledto one photodetector element of the photodetector.

In some embodiments where the photodetector may be a sparsephotodetector, the substituents or gaps of the scintillator may becoupled to the substituents or gaps of the photodetector. Variousembodiments according to the present disclosure may be ascertained toone skilled in the art. For example, the sparse photodetector mayinclude gaps only, and the substituents or gaps in the scintillator maysit on the gaps of the sparse photodetector and uncoupled tophotodetector elements. The coupling between the scintillator and thephotodetector that may be used in connection with the present systemdescribed herein are not exhaustive and are not limiting. Numerous otherchanges, substitutions, variations, alterations, and modifications maybe ascertained to one skilled in the art and it is intended that thepresent disclosure encompass all such changes, substitutions,variations, alterations, and modifications as falling within the scopeof the present disclosure.

The sparse detector according to some embodiments of the presentdisclosure may have several advantages. In some embodiments, compared toimaging devices with non-sparse detectors, the manufacture cost of theimaging devices with a sparse detector of the same field of view may bereduced. As mentioned above, the scintillators used in a medical imagingtechnology may be manufactured with a material containing a rare earthelement such as, for example, Lanthanum, Lutetium, Yttrium, etc.Scintillators containing rare earth elements may be expensive due tofactors including, for example, the difficulty of crystallization, thescarcity of economically exploitable ore deposits, etc. To achieve thesame field of view, the imaging devices with sparse detectors may reducethe amount of the material(s) for scintillators compared to the imagingdevices with non-sparse detectors. The imaging devices with sparsedetectors may keep high image quality and spatial resolution during thesame scanning time. The details regarding the image quality and spatialresolution will be further illustrated hereinafter.

In some embodiments, for the same amount of scintillator material,compared to non-sparse detectors, more sparse detectors may be made thannon-sparse detectors. Accordingly, using the same amount of scintillatormaterial, an imaging device with one or more sparse detectors may allowa larger or longer scan area; therefore, to scan a same area, an imagingdevice with one or more sparse detectors may take less time than animaging device without a sparse detector.

In some embodiments, when a same area is scanned, compared to an imagingdevices with non-sparse detectors, an imaging device with sparsedetectors may acquire less data (due to the absence of one or morescintillator crystals), and thereby reducing the consumption of thebandwidth or channels of the processing electronics. A sparse detectormay receive fewer projections than a non-sparse detector. The totalvolume of data to be processed may be reduced. Thus, the need for thebandwidth or channels of the processing electronics may be reduced.

FIG. 9 is a block diagram illustrating a processor 102 of an imagingsystem according to some embodiments of the present disclosure. Itshould be noted that a processor described below is merely provided forillustrating an example of the processor, and not intended to limit thespirit and scope of the present disclosure. The processor 102 may beconfigured to process the signals or instructions received from theimage devices 101, the terminal 103, the database 104, or other modulesor units in the system and it may send information to the modules orunits in the system. For example, it may perform functions of imageprocessing and controlling the operation of the imaging device 101. Itshould be noted that the above description about the structure of theprocessor 102 is merely an example, and is not intended to be limiting.In some embodiments, the processor 102 may include other modules, andthe modules may be integrated into one module to function together asneeded.

Referring to FIG. 9, the processor 102 may include an image processingmodule 901 and a control module 902. The image processing module 901 maybe configured to perform the functions including image reconstruction,image correction and preprocessing. The image processing module 901 mayreceive the signals or instructions from or send information to theimage devices 101, the terminal 103, the database 104, the controlmodule 902, or other modules or units in the system. More details aboutthe functions and structures of the image processing module 901 will bedescribed in FIG. 10.

The control module 902 may be configured to control different componentsof the imaging system in order to achieve optimal analysis of thetarget, and it may receive signals or instructions from or sendinformation to the image devices 101, the terminal 103, the database104, the image processing module 901, or other modules or units in thesystem. In some embodiments, the control module 902 may control theimage devices, for example, it may control the position of the detectormodules 301, the position of the target, the rotation speed of thegantry in the system. In some embodiments, the control module 902 maycontrol the data storage of the imaging system, including the storagelocation of data, the content of the data, the way to store, or thelike, or any combination thereof. For example, the control module 902may determinate when and/or in which format the imaging data are storedin the database 104, and/or determinate whether to store the imagingdata or the output data of the image processing module 901 in thedatabase 104. In some embodiments, the control module 902 may controlthe image processing module 901. For example, it may control the imageprocessing module 901 to select different reconstruction algorithmsand/or correction algorithms to process the imaging data. In someembodiments, the control module 902 may control the terminal 103. Forexample, the control module 902 may transmit some commands to terminal103, including the size of an image, the location of an image, or thelength of time an image remaining on a display screen. In someembodiments of the present disclosure, the image may be divided intoseveral sub-portions for display, and the control module 902 may controlthe number of the sub-portions.

It should be noted that the above description about the control module902 is merely an example, and not intended to limit the scope of thepresent disclosure. For persons having ordinary skills in the art,multiple variations and modifications may be made under the teachings ofthe present disclosure. For example, the control module 902 may alsocontrol data transmission of the imaging system. In some embodiments,the control module 902 may determinate when, how, and/or whether, theimaging data obtained from the imaging device 102 should be transmittedto the image processing module 901. In some embodiments, the controlmodule 902 may determinate whether the output information from theimaging device 101, the processor 102, the terminal 103, and thedatabase 104 should be transmitted in the network 105. In someembodiments, the control module 902 may determinate when, how, and/orwhether, the terminal 103 may receive input, or present outputinformation.

Although certain embodiments have been described above, theseembodiments have been presented by way of example only. It is obviousthat to those skilled in the art, after understanding the basicprinciples of the processor 102, the modules of the processor 102 may bemodified or varied without departing from the principles. Themodifications and variations are still within the scope of the presentdisclosure.

FIG. 10 is a block diagram illustrating an image processing module 901of the processor 102 according to some embodiments of the presentdisclosure. As illustrated in FIG. 10, the image processing module 901may include an image reconstruction unit 1001, an image correction unit1002, and a preprocessing unit 1003. It should be noted that the abovedescription about the structure of the image processing module 901 ismerely an example, and is not intended to be limiting. In someembodiments, the image processing module 901 may include other units,and the units may be integrated into one unit to function together asneeded.

Referring to FIG. 10, in some embodiments, the image reconstruction unit1001 may use a reconstruction algorithm to reconstruct the imaging datareceived. The reconstruction algorithm may be an analytic reconstructionalgorithm, an iterative reconstruction algorithm, or based on compressedsensing (CS). Analytic reconstruction algorithms may be a filteredbackprojection (FBP) algorithm, a back projection filtration (BPF)algorithm, a ρ-filtered layergram, or the like. Iterative reconstructionalgorithms may be an ordered subset expectation maximization (OSEM)algorithm, a maximum likelihood expectation maximization (MLEM)algorithm, or the like. In some embodiments, the algorithm mentionedabove may be combined with some support constraints. The supportconstraints may be predefined according to some factors such as thearrangement of scintillator crystals on a detector, or the arrangementof the detectors in the imaging devices, or other parameters such as,image resolution, sensitivity, stability, the size of the crystals, orthe like, or any combination thereof. It should be noted that anyreconstruction technique based on mathematic and statistical knowledgeof the data acquisition process, and geometry of the imaging systemdisclosed herein, is acceptable to be used in the image reconstructionunit 1001.

The image correction unit 1002 may be configured to modify the imagingdata generated from the imaging device 101, the image generated from theimage reconstruction unit 1001, or the like, or any combination thereof.For instance, the image correction unit 1002 may modify low-qualityimages resulting from, for example, calibration problems, detectorfailure, resolution and partial volume effects, patient motion,attenuation, scatter, or other factors that may influence the imagequality, or a combination thereof. In some embodiments, the imagecorrection unit 1002 may perform its function before, after, or incombination with the process of the image reconstruction. For example,when an iterative reconstruction algorithm is used in the process of theimage reconstruction, after each of iteration, the image correction unit1002 may perform correction. As another example, the image correctionunit may perform correction due to a physical characteristic of theimaging device including, for example, scatter, random coincidences,attenuation, normalization, etc., before image reconstruction, whileperform decay correction after the image is reconstructed. It should benoted that the above description about the image correction unit 1002 ismerely an example according to the present disclosure. Obviously, tothose skilled in the art, after understanding the basic principles ofthe image correction unit, the form and details of the process may bemodified or varied without departing from the principles. Themodifications and variations are still within the scope of the currentdisclosure described above.

Still referring to FIG. 10, in some embodiments, the preprocessing unit1003 may be configured to process the information used to reconstructand/or correct the image, or the like, or any combination thereof. Forexample, the preprocessing unit 1003 may determinate whether the outputdata from any step of image reconstruction and image correction meet apredefined threshold. Merely by way of example, the predefined thresholdmay be a desired image resolution, the total number of iterations initerative image reconstruction, clinically acceptable view of thetarget, and/or the acceptable degree of variation of the reconstructedimages, etc. In some embodiments, the preprocessing unit 1003 mayperform its function before, after, or in combination with the imageprocessing step and/or the image correction step.

While certain embodiments have been described above, these embodimentshave been presented by way of example only, and are not intended tolimit the scope of the present disclosure. Furthermore, variousomissions, substitutions, and changes in the form of the methods andsystems described herein may be made without departing from the spiritand the scope of the inventions.

FIG. 11 is a flowchart illustrating a process of image processingaccording to some embodiments of the present disclosure. It should benoted that the steps described here is merely an example, and is notintended to be limiting.

In step 1101, imaging data may be acquired. The acquisition may beaccomplished by the processor 102, or other modules or units capable ofacquiring data in the system. In some embodiments, the imaging data maybe acquired from the imaging device where a target may be underexamination. The imaging data acquired may be stored in the database 104or other modules or units capable of storing data. The storage format ofimaging data acquired may include, without limitation, listmode orsinogram.

In step 1102, the acquired imaging data may be preprocessed. The imagingdata acquired may be preprocessed by the preprocessing unit 1003 of theimage processing module 901 of the processor 102, or other modules orunits capable of processing data in the system. The imaging datapreprocessing may be performed in parallel to, or, as needed, after allimaging data has been acquired. The imaging data acquired may bepreprocessed in a listmode format or in a sinogram format, and thesinogram format may be converted from the listmode format. In someembodiments, the preprocessing of the acquired imaging data may include,without limitation, generating virtual scintillator units based onactual scintillator crystals, calculating the efficiency of virtualscintillator units and the line of response, estimating spatialresolution, etc. The preprocessed imaging data may be stored in thedatabase 104. The storage format of preprocessed imaging data mayinclude, without limitation, listmode or sinogram. The storage methodmay include, without limitation, sequential storage, linked storage,indexed storage, hashing storage, or the like, or a combination thereof.

In step 1103, image correction may be performed. The image correctionmay be accomplished by the image correction unit 1001 of the imageprocessing module 901 of the processor 102. Image correction mayinclude, without limitation, correction for random coincidences,estimation and subtraction of scattered photons, detector dead-timecorrection (after the detection of a photon, the detector may need to“cool down”), correction for radioactive nuclide decay,detector-sensitivity correction (for both inherent detector sensitivityand changes in sensitivity due to an angle of incidence), correction forattenuation due to absorption of coincidence events in the target orscattering out of the detector field of view, or the like, or acombination thereof. The corrected images may be stored in the database104. The storage method may include, without limitation, sequentialstorage, linked storage, indexed storage, hashing storage, or the like,or a combination thereof.

In step 1104, the corrected imaging data may be reconstructed by using areconstruction algorithm. The reconstruction of preprocessed imagingdata may be accomplished by the image reconstruction unit 1001 of theimage processing module 901 of the processor 102. The algorithm used toreconstruct images may include, without limitation, filteredback-projection (FBP), maximum likelihood Expectation maximum (MLEM),ordered subset expectation maximum (OSEM), or Complete Ordered SubsetExpectation Maximum (C-OSEM), or an algorithm based on compressedsensing (CS). In some embodiments, the reconstruction method may includetreating each detector as a separate entity, so that only coincidenceswithin a detector are detected. The imaging data from each detector maythen be reconstructed individually (2D reconstruction). In someembodiments, the reconstruction method may include allowing coincidencesto be detected between detectors as well as within detectors, thenreconstructing the entire volume together (3D reconstruction).Three-dimensional reconstruction techniques have better sensitivity(because more coincidences may be detected and used) and therefore lessnoise than two-dimensional reconstruction techniques. Three-dimensionalreconstruction techniques may be sensitive to the effects of scatter andrandom coincidences, and may consume greater computer resources,compared to two-dimensional reconstruction techniques. Thereconstruction of preprocessed imaging data may be performed in parallelto, or after all imaging data has been preprocessed, as needed. Thereconstruction may be conducted based on sinogram converted from part ofor all listmode preprocessed imaging data, or based on listmodepreprocessed imaging data directly. Reconstructed imaging data may bestored in the database 104. The storage method may include, withoutlimitation, sequential storage, linked storage, indexed storage, hashingstorage, or the like, or a combination thereof. Reconstructed images mayinclude a two-dimensional (2D) image, a three-dimensional (3D) volume, a3D volume over time (4D), etc. The system may output reconstructedimages. The reconstructed images may be provided for display, to aprinter, a computer network, or one or more other devices.

In some embodiments, the reconstructed image may be corrected usingimage correction algorithms. For example, decay correction may beperformed to compute the decay rate of the number or particles at alater time point relative to when they were measured. In someembodiments, the corrected image may be reconstructed again. In someembodiments, the corrected image may be stored and output.

It should be noted that the above description about the process ofprocessing imaging data and obtaining an image is merely an exampleaccording to the present disclosure. Obviously, to those skilled in theart, after understanding the basic principles of the process ofprocessing imaging data and obtaining an image, the form and details ofthe process may be modified or varied without departing from theprinciples.

FIG. 12 illustrates a process for processing imaging data and obtainingan image according to some embodiments of the present disclosure. Itshould be noted that the steps described here is merely an example, andis not intended to be limiting.

In step 1201, imaging data may be acquired. Based on the configurationof the scintillator crystals of the detectors according to a sparsityrule, a lookup table of the scintillator crystals may be obtained. Thisstep may be performed by the image processing module 901 of theprocessor 102 in the system. It should be noted that, the imaging datamay be obtained before, after, or around the same time that the lookuptable of the scintillator crystals is obtained. In some embodiments, thescintillator crystals of the detectors may be arranged in a uniformpattern, for example, a checkerboard pattern, a stepped pattern. In someembodiments, the scintillator crystals of the detectors may be arrangedby being spaced along the circumferential direction or along the axialdirection, or the both. The space in the row may be the same with ofdifferent from that in the column. In some embodiments, the scintillatorcrystals of the detectors may be arranged according to a sparsity rule.For instance, according to a sparsity rule, at most one scintillatorcrystal may be removed out of every two scintillator crystals in aplurality of scintillator crystals. See relevant description elsewherein the present disclosure. In some embodiments, the scintillatorcrystals of the detectors may be arranged randomly with a sparsitypredefined according to considerations including, for example, imageresolution, sensitivity, stability, the size of the crystals, or thelike, or any combination thereof. The sparsity may be any value between0 and 1. The lookup table obtained in the step may be a two-dimensionalmap that may be referred as a position map of scintillator crystals in adetector. In some embodiments, if one position is occupied by ascintillator crystal, the corresponding location in the lookup table maybe denoted as 1; while if the position is not occupied by a scintillatorcrystal, the corresponding location in the lookup table may be denotedas 0.

According to the lookup table generated in step 1201, virtualscintillator units may be generated in step 1202, and the step may beperformed by the preprocessing unit 1003 of the image processing module901 of the system. In some embodiments, the term “virtual scintillatorunit” may refer to a unit including what exists in two or more positions(for example, neighboring positions) along one direction, for example,along the axial direction of the gantry within which the detector isplaced. A position may refer to where a scintillator crystal may bepositioned. In a sparse detector, a position may be occupied by ascintillator crystal, or may be void (or referred to as gap) or occupiedby a substituent.

Merely by way of example, a virtual scintillator unit may include whatexists in two neighboring positions along the axial direction of thegantry within which the detector is placed. In some embodiments, thevirtual scintillator unit may include two scintillator crystals wheneach of the two positions is occupied by a scintillator crystal. In someembodiments, the virtual scintillator unit may include one scintillatorcrystal when one of the two positions is occupied by a scintillatorcrystal and the other position is a void (or gap) or occupied by asubstituent. In some embodiments, the virtual scintillator unit mayinclude no scintillator crystal when each of the two positions is a voidor occupied by a substituent.

A virtual scintillator unit may include an arbitrary number ofscintillator crystals, e.g., zero, one, two, three, four. In someembodiments, a virtual scintillator unit in a detector may include thesame number scintillator crystals. In some embodiments, at least twovirtual scintillator units in a detector may include different numbersof scintillator crystals.

In some embodiments, the imaging data acquired in step 1201 may bestored in the listmode, in some embodiments, the imaging data acquiredin step 1201 may be stored in sinogram.

In some embodiments, a virtual scintillator unit may be generated by theexpression below:Crystal_(N)(ia, Ra)=Crystal(ia , 2Ra)+Crystal(ia , 2Ra+1), Ra=0, 1, 2, .. . ,   (1)where (ia, Ra) may be denoted as a location on a detector wherein ia mayrepresent the number in the circumference direction, Ra may representthe number in the axial direction, Crystal_(N) may represent the virtualscintillator units, and Crystal(ia, 2Ra) may indicate whether thelocation (ia, 2Ra) may be occupied by a scintillator crystal.

In step 1203, the efficiency of the virtual scintillator units may becalculated. The step may be performed by the preprocessing unit 1003 ofthe image processing module 901 of the system. The efficiency of thevirtual scintillator units as used herein may refer to the number ofscintillator crystals in a virtual scintillator unit. In someembodiments, the efficiency of the virtual scintillator units may becalculated according to the lookup table established in step 1201, forexample,Ca(ia , Ra)=0.5*(Lut(ia, 2Ra)+Lut(ia, 2Ra+1)),   (2)where Ca may represent the efficiency of the virtual scintillator unit,Lut may represent the value in the lookup table. In some embodiments, ifone position is occupied by a scintillator crystal, the correspondinglocation in the lookup table may be denoted as 1, while if the positionis not occupied by a scintillator crystal, the corresponding location inthe lookup table may be denoted as 0. It should be noted that theexpression described above is merely an example, and is not intended tolimiting. In some embodiments, the expression above may be varied, forexample, the number of the term used to be added together may be largerthan two, the term may be in a same circumference direction, or be indifferent rows or in different columns, or the coefficient front may bevaried in some circumstance.

After the efficiency of the virtual scintillator units was generated,the efficiency of the line of response (LOR) of a coincidence event maybe calculated in step 1204. The step may be performed by thepreprocessing unit 1003 of the image processing module 901 of thesystem. The efficiency of the line of response used as herein may referto the product of the efficiency of virtual scintillators. In someembodiments, the efficiency of the line of response may be calculatedaccording to the expression below:C _(lor)=1/(Ca*Cb),   (3)where C_(lor) may represent the efficiency of the line of response , andCa and Cb may represent the efficiencies of the virtual scintillatorunits on which two photons of a coincidence event in the same line ofresponse (LOR) may incident respectively. It should be noted that theexpression described above is merely an example, and is not intended tolimiting. In some embodiments, the expression may be varied in somecircumstance.

In step 1205, image correction may be performed, and the step may beperformed by the image correction unit 1002 of the image processingmodule 901 or other modules or units capable of correcting image in thesystem. The image correction may include attenuation correction, scattercorrection, one or more other corrections that may influence the imagequality, or a combination thereof. Various methods for attenuationcorrection and scatter correction that are known in the art may be usedin connection with the present system. In some embodiments, a mapshowing attenuation properties of the target and/or its surroundingenvironment may be constructed and projected to correct photonattenuation in the reconstructed image, for example, a PET image. Insome embodiments, an attenuation map may be constructed based on imaginginformation generated by a different imaging modality of themulti-modality imaging system, such as MRI and/or CT.

Then, in step 1206, image reconstruction may be performed, and the stepmay be performed by the image reconstruction unit 1001 of the imageprocessing module 901 or other modules or units capable ofreconstructing image in the system. The reconstruction algorithm used inthe step may be an analytic reconstruction algorithm, an iterativereconstruction algorithms, or based on compressed sensing (CS). Analyticreconstruction algorithms may be a filtered backprojection (FBP)algorithm, a back projection filtration (BPF) algorithm, ap-filteredlayergram, or the like. Iterative reconstruction algorithms may be anordered subset expectation maximization (OSEM) algorithm, a maximumlikelihood expectation maximization (MLEM) algorithm, or the like. Insome embodiments, the algorithm mentioned above may be combined withsome support constraints. The support constraints may be predefinedaccording to some factors such as the arrangement of scintillatorcrystals on a detector, or the arrangement of the detectors in theimaging devices, or other parameters such as, image resolution,sensitivity, stability, the size of the crystals, or the like, or anycombination thereof.

For illustration purposes, the OSEM method may be described below. Inthis method, a pre-specified starting image may be needed, and theimaging data may be divided into several subsets, and the number ofsubsets may be set based on parameters including, for example, the timeof image reconstruction (e.g., the time available for imageconstruction), image quality, the size of detector, the amount ofimaging data, or the like, or a combination thereof. The iterativeprocess may be described as the expression below:

$\begin{matrix}{{f_{j}^{({n + 1})} = {\frac{f_{j}^{(n)}}{\sum\limits_{i_{k \in}s_{k}}M_{i_{k}j}}{\sum\limits_{k \in S}{M_{i_{k}j}\left( \frac{c_{lor}}{\sum\limits_{j_{p} \in L_{k}}{M_{i_{k}j_{p\;}}f_{j_{p}}^{(n)}}} \right)}}}},} & (4)\end{matrix}$

where f_(j) ^((n)) may represent the imaging data of the jth pixel inthe nth iteration, S_(k) may represent k th subset, L_(i) _(k) mayrepresent the i_(k) th LOR in k th subset, f_(jp) ^((n)) may representthe imaging data of the j_(p) th pixel of the L_(i) _(k) th LOR, M mayrepresent the system matrix, and C_(lor) may represent the efficiency ofthe line of response. After several times of iteration, the data of theimage that may meet the demands of the image quality may be obtained.

It should be noted that the above description about the process ofprocessing imaging data and obtaining an image is merely an exampleaccording to the present disclosure. Obviously, to those skilled in theart, after understanding the basic principles of the process ofprocessing imaging data and obtaining an image, the form and details ofthe process may be modified or varied without departing from theprinciples. In some embodiments, other steps may added in the process,for example, the intermediated data and/or the final data of the processmay be stored in the process, and the storage location may be indatabase 104 or other modules or units capable of storing data. In someembodiments, the order of the steps may be varied. For example, thesteps 1202, 1203, 1204 and the process of establishing a lookup tablemay be performed before the imaging data is acquired, and the system maybe corrected before scanning a target. The modifications and variationsare still within the scope of the current disclosure described above.

FIG. 13 illustrates an exemplary configuration of scintillator crystalsin a sparse detector according to some embodiments of the presentdisclosure. In such embodiments, a plurality of sparse detectors mayform a detector ring. Multiple detector rings may arrange along theaxial direction of a gantry. Referring to the figure, the horizontalaxis may represent the number of scintillator crystals along thecircumferential direction of the gantry, and the vertical axis mayrepresent the number of scintillator crystals in detector rings alongthe axial direction. Black dots in FIG. 13 may represent substituents orgaps, and blank area may represent scintillator crystals. As illustratedin FIG. 13, the distribution of the substituents or gaps may beaccording to a sparsity rule. The sparseness of the scintillatorcrystals in the sparse detector may be 10%. It should be noted that theconfiguration of scintillator crystals in a sparse detector used hereinis merely an example according to the present disclosure, not intendedto be limiting. Numerous other changes, substitutions, variations,alterations, and modifications may be ascertained to one skilled in theart and it is intended that the present disclosure encompass all suchchanges, substitutions, variations, alterations, and modifications asfalling within the scope of the present disclosure.

Having thus described the basic concepts, it may be rather apparent tothose skilled in the art after reading this detailed disclosure that theforegoing detailed disclosure is intended to be presented by way ofexample only and is not limiting. Various alterations, improvements, andmodifications may occur and are intended to those skilled in the art,though not expressly stated herein. These alterations, improvements, andmodifications are intended to be suggested by this disclosure, and arewithin the spirit and scope of the exemplary embodiments of thisdisclosure.

Moreover, certain terminology has been used to describe embodiments ofthe present disclosure. For example, the terms “one embodiment,” “anembodiment,” and/or “some embodiments” mean that a particular feature,structure or characteristic described in connection with the embodimentis included in at least one embodiment of the present disclosure.Therefore, it is emphasized and should be appreciated that two or morereferences to “an embodiment” or “one embodiment” or “an alternativeembodiment” in various portions of this specification are notnecessarily all referring to the same embodiment. Furthermore, theparticular features, structures or characteristics may be combined assuitable in one or more embodiments of the present disclosure.

Further, it will be appreciated by one skilled in the art, aspects ofthe present disclosure may be illustrated and described herein in any ofa number of patentable classes or context including any new and usefulprocess, machine, manufacture, or composition of matter, or any new anduseful improvement thereof. Accordingly, aspects of the presentdisclosure may be implemented entirely hardware, entirely software(including firmware, resident software, micro-code, etc.) or combiningsoftware and hardware implementation that may all generally be referredto herein as a “block,” “module,” “engine,” “unit,” “component,” or“system.” Furthermore, aspects of the present disclosure may take theform of a computer program product embodied in one or more computerreadable media having computer readable program code embodied thereon.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including electro-magnetic, optical, or thelike, or any suitable combination thereof. A computer readable signalmedium may be any computer readable medium that is not a computerreadable storage medium and that may communicate, propagate, ortransport a program for use by or in connection with an instructionexecution system, apparatus, or device. Program code embodied on acomputer readable signal medium may be transmitted using any appropriatemedium, including wireless, wireline, optical fiber cable, RF, or thelike, or any suitable combination of the foregoing.

Computer program code for carrying out operations for aspects of thepresent disclosure may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Scala, Smalltalk, Eiffel, JADE, Emerald, C++, C#, VB. NET,Python or the like, conventional procedural programming languages, suchas the “C” programming language, Visual Basic, Fortran 2003, Perl, COBOL2002, PHP, ABAP, dynamic programming languages such as Python, Ruby andGroovy, or other programming languages. The program code may executeentirely on the user's computer, partly on the user's computer, as astand-alone software package, partly on the user's computer and partlyon a remote computer or entirely on the remote computer or server. Inthe latter scenario, the remote computer may be connected to the user'scomputer through any type of network, including a local area network(LAN) or a wide area network (WAN), or the connection may be made to anexternal computer (for example, through the Internet using an InternetService Provider) or in a cloud computing environment or offered as aservice such as a Software as a Service (SaaS).

Furthermore, the recited order of processing elements or sequences, orthe use of numbers, letters, or other designations therefore, is notintended to limit the claimed processes and methods to any order exceptas may be specified in the claims. Although the above disclosurediscusses through various examples what is currently considered to be avariety of useful embodiments of the disclosure, it is to be understoodthat such detail is solely for that purpose, and that the presentdisclosure are not limited to the disclosed embodiments, but, on thecontrary, are intended to cover modifications and equivalentarrangements that are within the spirit and scope of the disclosedembodiments. For example, although the implementation of variouscomponents described above may be embodied in a hardware device, it mayalso be implemented as a software only solution—e.g., an installation onan existing server or mobile device.

Similarly, it should be appreciated that in the foregoing description ofembodiments of the present disclosure, various features are sometimesgrouped together in a single embodiment, figure, or description thereoffor the purpose of streamlining the disclosure aiding in theunderstanding of one or more of the various inventive embodiments. Thismethod of disclosure, however, is not to be interpreted as reflecting anintention that the claimed subject matter requires more features thanare expressly recited in each claim. Rather, inventive embodiments liein less than all features of a single foregoing disclosed embodiment.

We claim:
 1. An apparatus comprising: a sparse detector, the sparsedetector comprising: an array of scintillator crystals generatingscintillation in response to radiation, wherein the array ofscintillator crystals have a plurality of positions, a position is voidor occupied by a scintillator crystal or a block of a light-transmittingmaterial, and the array of scintillator crystals are arranged accordingto a sparsity rule that at least a portion of scintillator crystals ofthe array of scintillator crystals are spaced apart by one or morepositions that are void or occupied by one or more blocks of alight-transmitting material; and an array of photodetector elementsconfigured to generate an electrical signal in response to thescintillation, wherein at least a portion of the array of photodetectorsare coupled to the array of scintillator crystals; and a processorconfigured to: obtain imaging data from the sparse detector; generate aplurality of virtual scintillator units according to the sparsity rulerelated to the sparse detector, wherein a virtual scintillator unitcorresponds to two or more neighboring positions of the array ofscintillator crystals; calculate efficiency of a line of response basedon the plurality of virtual scintillator units; and generate, based onthe efficiency of the line of response and the imaging data, an image.2. The apparatus of claim 1, wherein the size of a block of the one ormore blocks of the light-transmitting material is substantially equal tothe size of a scintillator crystal of the array of scintillatorcrystals.
 3. The apparatus of claim 1, wherein the light-transmittingmaterial comprises glass.
 4. The apparatus of claim 1, wherein aposition that is void forms a gap between two scintillator crystals ofthe array of scintillator crystals.
 5. The apparatus of claim 4, whereinthe size of the gap is substantially equal to the size of onescintillator crystal of the array of scintillator crystals.
 6. Theapparatus of claim 1, wherein the sparsity rule defines that every twoneighboring positions include at least one scintillator crystal amongthe array of scintillator crystals.
 7. The apparatus of claim 1, whereinthe shape of a sparse detector is a block, an arc, a ring, a rectangle,or a polygon.
 8. The apparatus of claim 1, wherein the apparatuscomprises two detector modules parallel to each other, at least one ofthe two detector modules comprising one or more sparse detectors.
 9. Theapparatus of claim 1, wherein the apparatus comprises detector modulesforming a polygon, at least one of the detector modules comprising oneor more sparse detectors.
 10. The apparatus of claim 1, wherein theapparatus comprises sparse detectors forming a ring.
 11. An imagingsystem comprising: an apparatus comprising a plurality of sparsedetectors that generates imaging data, wherein each of the plurality ofsparse detectors comprises an array of scintillator crystals, whereinthe array of scintillator crystals have a plurality of positions, aposition is void or occupied by a scintillator crystal or a block of alight-transmitting material, and the array of scintillator crystals arearranged according to a sparsity rule that at least a portion ofscintillator crystals of the array of scintillator crystals are spacedapart by one or more positions that are void or occupied by one or moreblocks of a light-transmitting material; and a processor configured to:generate a plurality of virtual scintillator units according to thesparsity rule related to at least one of the plurality of sparsedetectors, wherein a virtual scintillator unit corresponds to two ormore neighboring positions of the array of scintillator crystals;calculate efficiency of the virtual scintillator units; calculateefficiency of a line of response based on the efficiency of the virtualscintillator units; and generate, based on the imaging data and theefficiency of the line of response, an image.
 12. The imaging system ofclaim 11, the imaging system being a Computed Tomography (CT) system, aDigital Radiography (DR) system, a Positron Emission Tomography (PET), aSingle Photon Emission Computed Tomography (SPECT)system, a ComputedTomography-Positron Emission Tomography (CT-PET) system, a ComputedTomography-Magnetic Resonance Imaging (CT-MRI) system, a PositronEmission Tomography-Magnetic Resonance Imaging (PET-MRI) system, aSingle Photon Emission Computed Tomography-Positron Emission Tomography(SPECT-PET) system, an X-ray security system or an X-ray foreign matterdetection system.
 13. A method comprising: acquiring imaging data usingan array of scintillator crystals, wherein the array of scintillatorcrystals have a plurality of positions, a position is void or occupiedby a scintillator crystal or a block of a light-transmitting material,and the array of scintillator crystals are arranged according to asparsity rule that at least a portion of scintillator crystals of thearray of scintillator crystals are spaced apart by one or more positionsthat are void or occupied by one or more blocks of a light-transmittingmaterial; generating, by a processor, a plurality of virtualscintillator units according to the sparsity rule related to the arrayof scintillator crystals, wherein a virtual scintillator unitcorresponds to two or more neighboring positions of the array ofscintillator crystals; calculating, by the processor, efficiency of thevirtual scintillator units; calculating, by the processor, efficiency ofa line of response based on the efficiency of the virtual scintillatorunits; and reconstructing, by the processor, an image based on thepreprocessed imaging data and the efficiency of the line of response.14. The method of claim 13, wherein the sparsity rule defines that everytwo neighboring positions include at least one scintillator crystalamong the array of scintillator crystals.
 15. The method of claim 13,further comprising performing image correction by the processor.
 16. Themethod of claim 13, wherein generating the plurality of virtualscintillator units according to the sparsity rule related to the arrayof scintillator crystals comprises: generating a lookup table relatingto the array of scintillator crystals; and generating the plurality ofvirtual scintillator units based on the lookup table.
 17. The method ofclaim 16, wherein calculating the efficiency of the virtual scintillatorunits comprises: for each of the virtual scintillator units, determiningan average value of a first value and a second value in the lookuptable, wherein the first value and the second value correspond to twolocations associated with the virtual scintillator unit.
 18. The methodof claim 17, wherein calculating the efficiency of the line of responsebased on the efficiency of the virtual scintillator units comprises:calculating a product of the efficiency of the virtual scintillatorunits, wherein the virtual scintillator units comprise a first virtualscintillator unit and a second virtual scintillator unit on which twophotons of a coincidence event in the line of response incidentrespectively; and calculating the efficiency of the line of responsebased on the product.